Nothing in particular - signposts are just markers that let you know where you are. Other examples in the area are Crankshaft Junction and Teakettle Junction - readily identifiable markings that let you know your current location.

It's just that these markers were put in place by individuals, so they chose to mark it in their own fashion - all our written signposts are the same, but some govt group decided on a common format that we could all recognize as authorotative.

Also, there used to be the 'painted rock' marker at the turnoff, but that was buried when NPS installed the pit toilets.